The present invention relates to wafer measurement apparatus and methods, and in particular relates to apparatus and methods for measuring the properties of one or more films on a wafer without the need for a wafer bath or complex wafer handling apparatus.
Chemical-mechanical polishing (CMP) is a well-known process in the semiconductor industry used to remove and planarize layers of material (xe2x80x9cfilmsxe2x80x9d) deposited on a semiconductor device to achieve a planar topography on the surface of the semiconductor device. To remove and planarize the layers of the deposited material, including dielectric and metal materials, CMP typically involves wetting a pad with a chemical slurry containing abrasive components and mechanically xe2x80x9cbuffingxe2x80x9d the front surface of the semiconductor device against the wetted pad to remove the layers of deposited materials on the front surface of the semiconductor device and planarize the surface.
Once polished, the wafer is cleaned at a cleaning station to remove any chemicals and slurry particulates that remain from the polishing process. Once cleaned, the wafers are brought to a measurement station to determine if the polisher produced the desired thickness and planarity of the top layers on the wafer. This typically involves performing an optical measurement that extracts the film thickness from measured reflectivity using thin-film analytical techniques. Often, it is preferred to make such measurements with the wafer upper surface immersed in water. For example, it is necessary to keep the wafer surface wet to prevent solid slurry residue from forming if the wafer is measured right after polishing but before cleaning.
An apparatus for measuring the film thickness of a wafer to determine if polishing is complete is described in U.S. Pat. No. 5,957,749 (the ""749 patent) and U.S. Pat. No. 6,045,433 (the ""433 patent). The ""749 and ""433 patents disclose an optical measurement station for measuring the film thickness of the one or more films on the wafer. The measurement station comprises a water bath (xe2x80x9cliquid holding unitxe2x80x9d) for receiving a wafer held by a gripping system. The liquid holding unit has a bottom surface, a portion of which is a window through which at least a portion of the top layer of the wafer is viewable. The gripping system grips the wafer and places it in the bath top surface down and at an angle relative to the horizontal. This tilting is necessary to allow any bubbles that might be trapped by the wafer top surface to escape, and so that the top surface can be viewed through the window. Once in the water bath, the wafer then needs to be tilted back to horizontal to perform the thickness measurement. An optical thickness measurement unit is in operative communication with the liquid holding unit and is used to measure the thickness of the top surface of the wafer through the window.
Unfortunately, the apparatus of the ""749 and ""433 patents has seven major disadvantages. The first is the need for a water bath for holding water in which the wafer can be placed during measurement. For large wafers, the bath must be quite large and hold a significant amount of water. In addition, this water needs to be clean and thus replaced frequently. The second disadvantage is that the wafer must be tilted when it is placed in the bath, and then made level once in the batch, which complicates the wafer measurement procedure and reduces throughput. A third disadvantage is that the gripper arm design is fairly complex because of the need to tilt the wafer when placing it in the water bath, and re-tilting the wafer to horizontal once in the bath. The fourth disadvantage is that the throughput of wafers is less than desirable because of the system complexity and the need to tilt the wafers with the specially designed wafer handler (xe2x80x9cgripper armxe2x80x9d). These disadvantages add cost and complexity to the system, as well as reduce the effectiveness of the apparatus in a manufacturing environment. The fifth disadvantage is that slurry particles and other contaminants in the water tend to sink to the bottom of the bath and settle on the surface of the window. Contamination on the window adversely affects the measurement, in particular if thin films of  less than 1000 A are measured. The sixth disadvantage is that parts of the top surface of the wafer are obscured by a support against which the wafer is held while upside down in the tank. A seventh disadvantage is that a wafer can accidentally be dropped (for example, when the gripper vacuum fails) and fall to the bottom of the tank, resulting in the need to stop the polisher to initiate a recovery procedure, or manually remove the wafer.
Accordingly, it would be advantageous to have an apparatus and associated methods of measuring the film thickness wafer without the above-described disadvantages.
The present invention relates to wafer measurement apparatus and methods, and in particular relates to apparatus and methods for measuring the film properties of one or more films on a wafer without the need for a wafer bath or complicated wafer handling apparatus.
Accordingly, a first aspect of the invention is wafer measurement apparatus for measuring a film thickness property of a wafer having an upper surface. The apparatus comprises a chuck having an upper surface for supporting the wafer, and a perimeter. A metrology module for measuring one or more wafer thickness properties, is arranged adjacent the chuck upper surface. The metrology module has a window with a lower surface arranged substantially parallel to the chuck upper surface. This arrangement defines an open volume between the chuck upper surface and the window lower surface. The apparatus further includes a water supply system in fluid communication with the open volume for flowing water through the open volume.
A second aspect of the invention is a wafer polishing system comprising the above-described wafer measurement apparatus and a wafer polishing system, such as a CMP tool, in operable communication with the wafer measurement apparatus.
A third aspect of the invention is a method of measuring a film thickness property of a wafer having an upper surface. The method comprises the steps of arranging the wafer in an open volume formed by a measurement window on one side and chuck upper surface on the opposite side. The wafer is placed on the chuck upper surface with the wafer upper surface facing the measurement window. The next step is flowing water through the open volume so as to fill the open volume. This is done in a manner that results in now bubbles being formed within the volume as water back-fills the volume, e.g., by flowing the water slowly at first so that the flow is established. The final step then involves measuring the film thickness property of the wafer through the measurement window.